Turbine blade with corrugated strut



Sept. 29, 1959 E. F. scHuM ETAL 2,906,495

TURBINE BLADE wI'n-x CORRUGATED STRUT Filed April 29, 1955 I INVENTORS EUGENE F. SCHUM HERMAN J. WIMMER BY [a y 3 ATTORNEYS United States Patent TURBINE BLADE WITH CORRUGATED STRUT Eugene F. Schum, North Olmsted, andv Herman J. Wimmer, Lakewood, Ohio, assignors to the United States of America as represented by the Secretary of the Navy Application April29, 1955,.SerialNo. 505,075

11 Claims. (Cl. 253-3915) (Granted under-Title 35, US. Code (1952),.sec. 266) The present invention relates to a turbine blade with a corrugated strut and more particularly to construction and assembly of such blades.

Heretofore, turbine blades have been made of a relatively large number of parts, and have required considerable machining. These parts have resulted in a relatively heavy. blade, which has resulted in a heavier engine due to the added weight necessary for the rotor as well as for the bladesthemselves.

An object of the present invention is; the provision of a turbine blade having a strut therein which is corrugated, the strut lending itself to rapid, accurate and inexpensive manufacture.

Another object is to provide a turbine blade having a sheet: metal base envelope; to permit multiple types: of rotor construction for cooling.

A further object of the invention is the provision. of a construction of turbine blades wherein a corrugated strut maybe securely fastened to the base.

Still another object is the provision of an improved rotor to. be used with. such a blade.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection withthe accompanying drawings whereirr:

Fig. 1 is a cross-sectional view of a preferred embodiment of the blade of the invention;

Fig. 2 is a perspective view, withparts broken away, of the turbine blade of the invention assembled With a split disc type rotor;

Fig. 3 is a perspective view, with parts broken away, of a modification; of the turbine blade of the invention assembled with a solid rotor;

Fig. 4 is a perspective view of the bottom of a turbine blade base of Fig. 2 with acorrugated strut assembled therewith, and

Fig. 5 is a rotor made to receive the blades of the present invention,

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views there is shown in Fig. l. a turbine blade having the usual shell 12 and acorrugated strut 14. Strut 14 is attached at certain of the corrugation tips 16 to the shell 12 by suitable means, such as by brazing. It will be noted that'not all of the tips of the corrugations of strut 14' are brazed to shell 12; those tips.- 16. which are not brazed do not protrude far enough to contact the inside of shell 12. Otherwise stated, a line connecting the tips. of the corrugation along either of the two cambers would not define a true airfoil camber line. The purpose of having the strut 14 joined to the shell 12 at only certain of the corrugation tips is to augment the cooling surface of the strut 14, to thus in- 2,906,495 Patented Sept. 29, 1959 sure lower strut temperatures. The number. of cornlgar tions that make contact will depend on the centrifugal.

load of the shell and the necessary braze area. torestrain. this load. As will: be set, forth more fully hereinafter, cooling air is supplied to the blade 10 through its base, and. will travelv between the shell 12,. and strut 14.

In Fig. 2, the blade 10. is shown mounted in a. rotor:

comprising two spacedv discs, only one disc 18 being shown. Thediscs have a plurality of slots.therein extending generally axially of the rotor. Each of. the slots- (see Fig. 5 comprises a trapezoidal inner. part with the longer base of the trapezoid closer to the center of the rotor and with. a rectangular slot extending outwardly from the.

shorter. base of. the trapezoid- A trapezoidal or dovetail. base is. positioned in the trapezoidal part of the slot 20, the base comprising. two complementary parts 22 24,,

with. the strut: 1.4 extending from between. the parts 22.

and 2,4 outwardly through. the rectangular part of the slot 20. A sheetmetal base envelope 2.6 lies. between the base androtor and has bottom and side portions. in. contact with the sides of the slot 20, anda bridge part 28. extending from the sides of the slot 20 towards the. strut 14. The bridge part bridges the gapin the periphery of the rotor, and forms a plenum chamber 30 above the two-part base. The shell 12 is joined to the bridge 28. of envelope 26 at 26.,v communication being provided between the plenum chamber 30 and the interior of the blade 10. Slots 32, in the, base parts 20 and 22 communicate the space between the rotor discs andv the plenum chamber 30. Cooling air may flow from the space between the discs, through the slots 32, into the plenum chamber 30 and thence into the blade 10,

In Fig. 3, the turbine blade 10v and the base envelope 26 are the same as previously described. The strut 14 is held in a base having two parts 34 and 36, and parts 34: and 36 being in this embodiment solid; i.e., there are no, slots therein. A shroud 37 is. attached'to the solid type rotor 40, and. cooling air may be supplied to the space between the shroud 37 and rotor 40. It will then proceed into the plenum chamber 30, and into the blade 10, as before.

The means for joining the strut 14. to the base parts 22 and 2,4; or 3.4 and 36 are shown. in Fig. 4. The inner end of the strut 14 has been slit, and tabs 38. for-med. thereby. These. tabs 38. are then bent so that they areat. approximately to a plane through the span of strut 14, andare brazed to the parts 22 and 24 or 34 and 36- of the base, the parts then being brazed to eachother, so that the-three pieces are-thus united.

In order to accommodate larger dovetail bases and maintainthedesired number of blades 10; the rotor may have the dovetail slots therein at different diameters of the rotor. This. construction is illustrated in Fig. 5, wherein the rotor 42. has dovetail slots 44 and 46 near the periphery, and. alternate dovetail slots 48 and; 50; nearer the center of the rotor. It will be understood, of course, that rotor 42 may be either the solidtype, asillusgateg in Fig. 3 or the split disc type as illustrated in It will thus be seen. that the construction. herein per-. mits the rapid and relatively easy manufacture of a rotor and blade assembly. which is. relatively. light, strong, and which provides for. the cooling of the blade.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that Within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is: I i

l. A turbine blade comprising an outer airfoil-shaped shell, a corrugated supporting strut for said shell having corrugations extending span-wise of said blade, said strut having an inner end and an outer end and being located with said outer end within said shell and with said inner end protruding from said shell, means joining fewer than the total number of the tips of said corrugations to the inner surface of said shell, a base for holding said strut comprising two complementary parts engaging said strut on opposite sides of the inner end thereof, the inner end of said strut having tabs thereon, said tabs lying against the surface of said base opposite said shell.

2. The device of claim 1, in which some of said tabs lie against one of said base parts and the remainder of said tabs lie against the other of said base parts.

3. In a turbine, a rotor, a plurality of axially extending slots extending through the periphery of said rotor, each of said slots having in cross section in a plane parallel to the plane of said rotor a trapezoidal inner part with the longer base of the trapezoid closer to the center of the rotor and a rectangular outer part extending from the shorter base of the trapezoidal part of the slot through the periphery of the rotor, a turbine blade in each of said slots comprising a base having a trapezoidal cross section in a plane parallel to the plane of said rotor, said trapezoidal cross-section being similar to and of smaller area than the trapezoidal part of said slot, said base being within and in mating relationship with the trapezoidal part of said slot and having two complementary parts, said base being constructed and arranged to hold a strut held between said complementary parts and extending therefrom through the rectangular part of said slot, the thickness of said strut in the circumferential direction of said rotor being less than the width of the rectangular part of said slot in the circumferential direction of said rotor, whereby a space is provided between said strut and the sides of the rectangular part of said slot, an envelope contacting the side surfaces of said slot and having bottom portions extending from the ends of the longer base of the trapezoidal part of said slot toward each other and in contact with the longer base, said envelope in the trapezoidal part of said slot lying between said base and the surfaces of said slot, said envelope being of such thinness as to leave said space substantially undiminished and having a bridge portion extending between the sides of the rectangular portion of said slot, said bridge portion having an opening therein adapted to permit said strut to extend therethrough, said envelope thereby defining a plenum chamber in the rectangular part of said slot within said envelope, an airfoil-shaped shell extending outwardly from the bridge portion of said envelope, said strut extending into said shell and being adapted to contact said shell only at spaced points being joined to the inner surface of said shell at said spaced points thereby to support said shell and to provide spaces between said strut and said shell, said spaces being in communication with said plenum chamber, and means communicating with said plenum chamber being adapted to supply fluid to said plenum chamber.

4. The apparatus of claim 3, said rotor comprising two spaced discs, the base having a passage therethrough and the envelope having an opening between the bottom portions thereof in juxtaposition with the passage through said base, whereby the fluid supply means communicateswith said plenum chamber.

5. The apparatus of claim 3, said last mentioned means comprising an annular radially inwardly extending shroud attached to said rotor at its periphery.

6. The apparatus of claim 3, said strut having tabs at its inner end lying in contact with the surfaces of the component parts of the base located adjacent said longer base of the trapezoidal inner part of said axially extending slot.

7. The apparatus of claim 3, the trapezoidal parts of said slots being arranged about the axis of rotation of the rotor in a plurality of concentric groups, each group being arranged at different diameters of the rotor with the trapezoidal parts in each group being symmetrically arranged about said axis of rotation and with adjacent slots being at ditferent diameters of the rotor.

8. The apparatus of claim 3, the trapezoidal parts of said slots being arranged about the axis of rotation of the rotor in two concentric groups, each group being arranged at different diameters of the rotor with the trapezoidal parts in each group being symmetrically arranged about said axis of rotation and with adjacent slots being at different diameters of the rotor.

9. The device of claim 1 in which some of said tabs lie against one of said base parts and the remainder of said tabs lie against the other of said base parts, means joining said tabs to said base parts thereby preventing withdrawal of said strut from said base under the urging of centrifugal force.

10. The method of making, assembling and securing a blade for a turbine, compressor, blower or the like, to

a split-disc rotor having axially extending blade slots through its periphery with the blade slots having in crosssection in a plane parallel to the plane of said rotor a trapezoidal inner part with the longer base of the trapezoid closest to the center of the rotor and a rectangular outer part extending from the short base of the trapezoid through the periphery of the rotor, the walls of said blade slots having thereby rectangular side surfaces extending substantially radially of said rotor and sloping side surfaces extending at an angle to said rectangular portions; said method comprising the steps of forming an outer shell in the shape of an airfoil from thin heat-resistant sheet metal, forming a corrugatedstrut having a length greater than the depth of the blade slots said depth being measured radially of the rotor and such strut having a maximum over-all depth of corrugation less than the Width of the rectangular outer part of the blade slot said width being measured in a plane parallel to the plane of the rotor and said strut further having such variable depth of corrugation to permit said strut to be inserted within said outer shell such that the corrugations extend spanwise of said shell and fewer than the total number of the tips of said corrugations contact the inner surface of said outer shell, forming a dovetail base in two complementary parts, said parts when placed in juxtaposition having the shape of a right trapezoidal prism having two parallel faces, the trapezoidal cross-section thereof being similar to and of smaller area than the area of the trapezoidal part of the blade slot, there being a corrugated aperture passing through said dovetail base extending through the parallel faces thereof said aperture being defined by the opposing surfaces of the two complementary parts and in addition there being a plurality of slots located in said parts of said dovetail base to either side of said corrugated aperture, said slots passing through said dovetail base and extending through the parallel faces thereof,

forming a one piece base envelope of sheet metal adapted to be placed in juxtaposition with the blade slot, said envelope having sloping and rectangular side portions to contact the sloping and rectangular side surfaces of said blade slot and being coextensive therewith with each sloping side portion having a bottom portion attached thereto to contact the longer base of the trapezoidal inner part of the blade slot and having a bridge portion extending between said side portions with an aperture formed in said bridge portion, the periphery of said aperture being constructed and arranged to engage one end of said outer shell, inserting one end of said corrugated strut between the complementary parts of said dovetail base in juxtaposition with said corrugated aperture with a small portion of said strut projecting from the larger of said parallel faces and the major portion of said strut projecting from the smaller of said parallel bases, slotting the small projecting strut portion to form tabs, bending said tabs to a angle, said tabs thereby lying against the larger of the parallel faces of said dovetail base, joining said complementary parts to one another then joining said corrugaiions to said joined complementary parts and joining said tabs to the larger of the parallel faces of said dovetail base resulting in an assembly, inserting said assembly in said envelope with one end of said corrugated strut projecting through the aperture in the bridge portion of said envelope and with the sloping side surfaces of said dovetail base being in juxtaposition with the sloping side surfaces of said envelope, telescoping the outer shell over the portion of said corrugated strut projecting beyond the bridge portion of said envelope, joining to the inner surface of said outer shell those tips of said corrugations making contact with said inner surface or" said outer shell, joining said envelope to said dovetail base, joining said outer shell to the periphery of said aperture in said bridge portion of said envelope, inserting the composite unit of strut, dovetail base, envelope and outer shell into and in juxtaposition with said blade slot and joining said composite unit to said split-disc rotor.

11. The method of making, assembling and securing a blade for a turbine, compressor, blower or the like, to a split-disc rotor having axially extending blade slots through its periphery with the blade slots having in crosssection in a plane parallel to the plane of said rotor a trapezoidal inner part with the longer base of the trapezoid closest to the center of the rotor and a rectangular outer part extending from the short base of the trapezoid through the periphery of the rotor, the walls of said blade slots having thereby rectangular side surfaces extending substantially radially of said rotor and sloping side surfaces extending at an angle to said rectangular portions, said method comprising the steps of forming an outer shell in the shape of an airfoil from thin heat-resistant sheet metal, forming a corrugated strut having a length greater than the depth of the blade slots said depth being measured radially of the rotor and such strut having a maximum over-all depth of corrugation less than the width of the rectangular outer part of the blade slot said width being measured in a plane parallel to the plane of the rotor and said strut further having such variable depth of corrugation to permit said strut to be inserted Within said outer shell such that the corrugations extend spanwise of said shell and fewer than the total number of the tips of said corrugations contact the inner surface of said outer shell, forming a dovetail base in the shape of a right trapezoidal prism having two parallel faces, the trapezoidal cross-section thereof being similar to and the area thereof being smaller than the area of the trapezoidal part of the blade slot, there being a corrugated aperture passing through said dovetail base extending through the parallel faces thereof and in addition there being a plurality of slots located to either side of said corrugated aperture and passing through said dovetail base and extending through the parallel faces thereof, forming a base envelope of sheet metal adapted to be mated with the blade slot having sloping and rectangular side portions to contact the sloping and rectangular side surfaces of said blade slot being coextensive therewith with each sloping side portion having a bottom portion attached thereto to contact the longer base of the trapezoidal inner part of the blade slot and having a bridge portion extending between said side portions with an aperture formed in said bridge portion, the periphery of said aperture being constructed and arranged to engage one end of said outer shell, inserting one end of said corrugated strut through said corrugated aperture with a small portion of said strut projecting from the larger of said parallel faces and the major portion of said strut projecting from the smaller of said parallel bases, slotting the small projecting strut portion to form tabs, bending said tabs to a angle, said tabs lying against the larger of the parallel faces of said dovetail base, joining said corrugations to said dovetail base and joining said tabs to the larger of the parallel faces of said dovetail base resulting in an assembly, inserting said assembly in said envelope with one end of said corrugated strut projecting through the aperture in the bridge portion of said envelope and with the sloping side surfaces of said dovetail base being in juxtaposition with the sloping side surfaces of said envelope, telescoping the outer shell over the portion of said corrugated strut projecting beyond the bridge portion, joining to the inner surface of said outer shell the tips of said corrugations making contact with said inner surface of said outer shell, joining said envelope to said dovetail base, joining said outer shell to the periphery of said aperture in said bridge portion of said envelope, inserting the composite unit of strut, dovetail base, envelope and outer shell into and in juxtaposition with said blade slot and joining said composite unit to said split-disc rotor.

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